A telephone system includes what is commonly referred to as "outside plant". The outside plant comprises the physical facilities (wires, cables, cross-connect boxes) that interconnect telephone station sets with a central office switch. FIG. 1, more particularly, shows a schematic diagram of typical outside plant facilities that are used to connect telephone subscribers to a local Central Office (CO) 100. Such outside plant facilities include multiconductor cables, e.g., cables 41 through 45, each of which includes a large number of pairs of copper wires twisted together. In general, one such pair is used to provide telephone service to one subscriber. Cables are identified as to their proximity to CO 100, e.g., F1 cables 41 and 42 and F2 cables 43, 44 and 45, separated by cross-connect terminals 46 and 47. F1 cables 41 and 42 are often called feeder cables, since they connect to terminals located at one side of a Main Distributing Frame (MDF) contained in CO. The terminals at the other side of the MI)F connect to respective port, or line, circuits, of Originating Equipment (OE) associated with switching equipment that is also located in the CO. It is the port circuit that presents dial tone to an associated telephone station set which is in an off-hook state and which is connected to the port circuit via the outside plant facilities.
Cross-connect terminals 46 and 47, in particular, are devices for connecting wire pairs to each other. They have one set of binding posts for connecting wire pairs from the central office (the IN side set) and another set of binding posts for connecting wire pairs from the opposite (field) direction (the OUT side set). In addition, wire jumpers are used to connect selected IN pairs to selected OUT pairs, thereby effectuating a physical connection between distribution cable pairs and feeder cable pairs.
At selected points along cables 41 through 45 are serving terminals 48. These serving terminals also have binding posts for connecting cable pairs to customer service wires such as drop wires 49 and 50 connected to customer living units 51 and 53, respectively. Distribution, or serving, terminals are typically located at concentrations of subscriber living units and can be located on telephone poles, in pedestals or on customers' premises.
While connections at cross-connect and serving terminals are maintained for a relatively long period of time, customers do move, thereby causing outside facilities to be reassigned. In central offices serving hundreds of thousands of customers, such reassignments of outside facilities constitutes a major, labor-intensive activity. Maximizing the efficiency and minimizing the cost of such reassignments has, therefore, become an important telephone company activity. For example, the telephone company employs very large databases to inventory the status of each element (i.e., cables, pairs, cross connect and serving terminals, etc) forming its outside plant facilities so that it may readily identify which elements are idle, in use (working), spare, defective, etc. The telephone company also employs other large databases to track and assign the unique connections from the central office main distributing frame to respective living units, e.g., LUs 51 through 53.
For example, TN:OE:F1 . . . FN:ST:Home Address: Billing Address:Listing Address: is the format of the fields of a database record, the contents of which define a unique connection, where TN is the assigned Telephone Number; OE is the address of the Originating Equipment (i.e., telephone switch input port or line circuit); FI . . . FN identify the cables pairs involved in the connection as well as the cross connect terminals and associated binding posts at which the cable pairs are connected; and ST identifies the serving terminal and associated binding post for the connection of the drop wire to the living unit (the remaining fields are self explanatory). Thus, the connection starts at the OE, the source of dial tone, and ends at a particular binding post of the serving terminal. (It is often the case that a number of levels of outside cables, (F1, F2 . . . Fn) are needed to implement telephone service to a telephone station set.)
Providing telephone service to a subscriber's living unit thus entails assigning in a database the necessary wires, terminals, binding posts and subscriber service wires to create a complete and continuous transmission circuit (local loop) between the local CO and subscriber's telephone station set. Once the assignment is made in the database, then the corresponding physical connections have to be made in the field at the time that service is to be initiated.
It can be appreciated from the foregoing that the amount of data that is stored in such databases is enormous and that the cost of provisioning and maintaining such databases is indeed very expensive.
Steps have been taken, however, to simplify such outside plant facilities. Specifically, the telephone companies have been installing electronic signal distributors operative for multiplexing an appreciable number of circuits over a few wires, e.g., two pairs of wires, thereby eliminating the need to employ cables containing large numbers of wire pairs. In this way a cable, for example, cable 41, may be replaced by four wires (two pairs) to interconnect a number of OEs at the CO and a Subscriber Loop Carrier (SLC) system located at a cross connect terminal, e.g., CCT 46. Such a SLC may be, for example, the model SLC2000 available from AT&T. Briefly, one pair of the four wires to the SLC may be used to transport circuit information from the CO to the input of the SLC, in which the information is contained in a respective one of a plurality of time-based channels (i.e. time slots). The SLC, in turn, demultiplexes the channels (or time slots) and delivers the information contained therein to respective ones of its associated terminals (binding posts). Such terminals include a terminal connected to a pair of wires extending to a living unit. The SLC also multiplexes information inputted at its associated terminals onto various time-based channels transmitted over the pair of wires for delivery to respective OEs at the associated CO.
In addition, a SLC may be disposed at each serving terminal and each intermediate cross connect terminal to greatly reduce the number of such large cables. However, such a reduction in the number of large cables does not lead to like reduction in the amount of data that is stored in the aforementioned databases. The reason for this is that an assignment still includes all of the elements involved in establishing a connection from an OE to a serving terminal binding post even though the end-to-end connection is derived from time-based apparatus, i.e. time slots.